If something you have done pays off, it is successful.

All her hard work paid off in the end, and she finally passed the exam. 她的所有努力最终得到了回报，她终于通过了考试。

to pay back money that you owe

We should be able to pay off the debt within two years. 我们应该能在两年内还清债务。

If your employer pays you off, they pay you for the last time and then end your job, because you are not needed or there is not enough money to pay you in the future.

to give someone money so that they will not do or say something, or so that they will go away

There were rumours that key witnesses had been paid off to keep quiet. 传言说关键证人都被收买，不肯出面作证。